feat: add support for customerio source email subscribed event

[Gauravudia]

What are the changes introduced in this PR?

Write a brief explainer on your code changes.

What is the related Linear task?

Resolves INT-2344

Please explain the objectives of your changes below

Put down any required details on the broader aspect of your changes. If there are any dependent changes, mandatorily mention them here

Any changes to existing capabilities/behaviour, mention the reason & what are the changes ?

N/A

Any new dependencies introduced with this change?

N/A

Any new generic utility introduced or modified. Please explain the changes.

N/A

Any technical or performance related pointers to consider with the change?

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@coderabbitai review

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Developer checklist

• My code follows the style guidelines of this project

• No breaking changes are being introduced.

• All related docs linked with the PR?

• All changes manually tested?

• Any documentation changes needed with this change?

• Is the PR limited to 10 file changes?

• Is the PR limited to one linear task?

• Are relevant unit and component test-cases added in new readability format?

Reviewer checklist

• Is the type of change in the PR title appropriate as per the changes?

• Verified that there are no credentials or confidential data exposed with the changes.

[devops-github-rudderstack]

Test report for this run is available at: https://test-integrations-dev.s3.amazonaws.com/integrations-test-reports/rudder-transformer/3679/test-report.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.55%. Comparing base (ec0bffe) to head (92eef03).
Report is 7 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3679   +/-   ##
========================================
  Coverage    88.55%   88.55%           
========================================
  Files          585      585           
  Lines        31910    31910           
  Branches      7613     7615    +2     
========================================
  Hits         28258    28258           
+ Misses        3359     3329   -30     
- Partials       293      323   +30     

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[sonarcloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
91.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud